Systems and methods for in-line thermal flattening and enameling of steel sheets

ABSTRACT

The present disclosure provides systems and methods for in-line thermal flattening and enameling of steel sheets. The systems and methods include an in-line thermal flattening of a feed stock steel sheet and a subsequent enamel coating of the steel sheet. The resulting enamel coated steel sheet has improved flatness compared with other coated steel sheets that are enamel coated but do not undergo the in-line thermal flattening. The systems and methods allow the use of less expensive source materials without sacrificing quality in the finished enameled product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/595,295, filed Dec. 6, 2017, which is incorporated by reference inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

N/A

BACKGROUND

Certain steel vitreous enameling procedures require highlystress-relieved and extremely flat starting material in order to achievea final coated product that has minimal deviation from flatness. Onesuch enameling procedure is a two-step, two-fire porcelain enamelingprocess. It is difficult to determine prior to the enameling whether astarting material has sufficient stress relief and flatness to achievethe desired minimal deviation. Historically, cold rolled commercialsteel that has been batch annealed has produced coated products withdeviations from flatness that have exceeded needs. The solution to thisproblem has historically been to source continuously-annealed steel,which comes at a significantly increased cost.

Typical methods for correcting a lack of flatness in batch-annealedsteel include temper rolling, roller leveling, tension leveling, andstretch leveling.

Temper rolling is primarily aimed at hardening annealed steel andremoving yield-point elongation (kinking), but it has the secondarybenefit of correcting flatness. Temper rolling is not to be confusedwith tempering, which is an unrelated heat treatment process in hotforging that has a similar name. Temper rolling involves a 0.5-1.5%reduction in thickness using a single or double series of rolls toprovide a small amount of cold work to the steel.

Roller leveling is the most inexpensive way to correct imperfections inflatness on batch annealed material. Roller leveling is typicallyinstalled at the start of the processing line. (i.e., the coating line).Roller leveling involves about 0.25-0.5% cold reduction through a seriesof small rolls in a cassette.

Tension leveling is another common approach to shape correction. Tensionleveling is essentially roller leveling with an added tension applied.Tension leveling is typically installed as a stand-alone operation orpart of a continuous annealing line. Tension leveling can achieve up to1.5% cold reduction with fewer rolls by the addition of strip tension tothe roller leveler configuration.

Stretch levelling is the least common but most effective method of shapecorrection. It is typically installed as a stand-alone operation andused in specialty steel and alloys. It can achieve up to 3% coldreduction with no rolls by using extremely high strip tension.

These means of correcting flatness are mentioned as potential solutionsto the problem of lack of flatness in batch-annealed steel that isrequired for certain enameling processes. However, when attempted, thesemeans of correcting flatness are insufficient to overcome the lack offlatness in batch-annealed steel. Conventional flattening processes areunpredictable in their ability to convert batch-annealed steel into astate suitable for certain enameled steels.

Accordingly, a need exists for systems and methods that allowcold-rolled, batch-annealed steel to be received at a manufacturingfacility and coated with a two-step, two-fire enameling process toprovide a product that has sufficient flatness.

BRIEF SUMMARY

The present disclosure provides systems and methods for in-line thermalflattening and enameling of steel sheets.

In an aspect, the present disclosure provides a method of producing anenameled steel sheet having an enamel coating on both sides. The methodincludes: a) in-line thermal flattening a feed stock steel sheet,thereby producing a thermally-flattened steel sheet; and b) subsequentto step a), enamel coating the thermally-flattened steel sheet on bothsides, thereby producing the enameled steel sheet having the enamelcoating on both sides, wherein executing the enamel coating of step b)directly to the feed stock steel sheet without the in-line thermalflattening of step a) produces a comparison enameled steel sheet havingthe enamel coating on both side, the comparison enameled steel sheethaving a maximum deviation from flat of 0.5 mm or greater when apressure of 20 kg/m² is applied, the enameled steel sheet having amaximum deviation from flat of less than 0.5 mm when a pressure of 20kg/m² is applied.

In another aspect, the present disclosure provides a system. The systemincludes a source zone, an in-line thermal flatting zone, a two-sideenameling zone, and a product removal zone. The source zone is forreceiving a source produce to be processed. The in-line thermalflattening zone is downstream of the source zone. The two-side enamelingzone is downstream of the in-line thermal flattening zone. The productremoval zone is for removing finished products from the system and isdownstream of the two-side enameling zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system, in accordance with aspects of thepresent disclosure.

FIG. 2 is a schematic of an in-line thermal flattening zone of thesystem, in accordance with aspects of the present disclosure.

FIG. 3 is a schematic of a two-side enameling zone of the system, inaccordance with aspects of the present disclosure.

FIG. 4 is an exemplary temperature and tension profile for the systemsand methods, in accordance with aspects of the present disclosure.

FIG. 5 is a flowchart of a method, in accordance with aspects of thepresent disclosure.

DETAILED DESCRIPTION

Before the present invention is described in further detail, it is to beunderstood that the invention is not limited to the particularembodiments described. It is also to be understood that the terminologyused herein is for the purpose of describing particular embodimentsonly, and is not intended to be limiting. The scope of the presentinvention will be limited only by the claims. As used herein, thesingular forms “a”, “an”, and “the” include plural embodiments unlessthe context clearly dictates otherwise.

It should be apparent to those skilled in the art that many additionalmodifications beside those already described are possible withoutdeparting from the inventive concepts. In interpreting this disclosure,all terms should be interpreted in the broadest possible mannerconsistent with the context. Variations of the term “comprising”,“including”, or “having” should be interpreted as referring to elements,components, or steps in a non-exclusive manner, so the referencedelements, components, or steps may be combined with other elements,components, or steps that are not expressly referenced. Embodimentsreferenced as “comprising”, “including”, or “having” certain elementsare also contemplated as “consisting essentially of” and “consisting of”those elements, unless the context clearly dictates otherwise. It shouldbe appreciated that aspects of the disclosure that are described withrespect to a system are applicable to the methods, and vice versa,unless the context explicitly dictates otherwise.

Numeric ranges disclosed herein are inclusive of their endpoints. Forexample, a numeric range of between 1 and 10 includes the values 1 and10. When a series of numeric ranges are disclosed for a given value, thepresent disclosure expressly contemplates ranges including allcombinations of the upper and lower bounds of those ranges. For example,a numeric range of between 1 and 10 or between 2 and 9 is intended toinclude the numeric ranges of between 1 and 9 and between 2 and 10.

The terms “upstream” and “downstream” refer to the direction of productmovement through a system. If the product (i.e., steel sheet) interactswith a first component before interacting with a second component as itmoves through a system, then the first component is upstream of thesecond component (and the second component is downstream of the firstcomponent).

Referring to FIG. 1, this disclosure provides a system 10 for in-linethermal flattening and two-side enameling of a steel sheet 20. Thesystem 10 includes a source zone 12, an in-line thermal flattening zone14, a two-side enameling zone 16, and a product removal zone 18.

The source zone 12 can include components known to those having ordinaryskill in the art to be useful for loading steel sheet into the system10. For example, an arm for receiving a roll of cold-rolled steel can bepresent in the source zone 12.

Referring to FIG. 2, one implementation of the in-line thermalflattening zone 14 is illustrated. The in-line thermal flattening zone14 can include a furnace 30 having isolated atmosphere 34 and at leasttwo tensioning rolls 32. The furnace 30 includes a heat source 36. Theheat source 36 can be a radiant heat source, a convection heat transferheat source, or a combination thereof. The heat source 36 can beelectric or gas. The heat source 36 can be configured to, in the casewhere combustion is utilized (i.e., gas), isolate the products ofcombustion (i.e., CO₂, etc.) from the material being heated. The furnace30 can be configured to operate at temperatures and with atmospheresdescribed below with respect to method 100. The at least two tensioningrolls 32 can be configured to provide the tensions described below withrespect to method 100. The direction of tension is illustrated by arrow40. The in-line thermal flattening zone 14 can include other rollers orvarious other positioning implements for aiding in alignment of thesteel sheet.

Referring to FIG. 3, one implementation of the two-side enameling zone14 is illustrated. The two-side enameling zone 16 is understood by thosehaving ordinary skill in the porcelain enameling arts to encompass avariety of structural arrangements and the description that follows ismerely one of the contemplated arrangements. The two-side enameling zone16 can include a first slurry applicator 50, a first furnace catenary 52configured to maintain tensions described below, a first furnace 54having a first heat source 56 configured to apply the heat describedbelow, a second slurry applicator 60, a second furnace catenary 62configured to maintain tensions described below, and a second furnace 64having a second heat source 56 configured to apply the heat describedbelow. The first furnace 54 and the second furnace 64 are separate anddistinct furnaces. The first furnace 54 and second furnaces 64 can havedust free atmospheres 66, which can be the same or differentatmospheres. The first heat source 56 and/or the second heat source 56can include radiant tubes. The radiant tubes can be natural gas fired.The first slurry applicator 50 and the second slurry applicator 60 applyslurry 68 to the steel sheet 20. The slurry 68 can be the same ordifferent when applied to opposite sides of the steel sheet 20. Theslurry 68 can be a porcelain enamel slip that is composed primarily ofwater and silicon dioxide.

The product removal zone 18 can include various cutting devices, rollingdevices, stacking devices, and other means of manipulating the finishedproduct to be suitable for transportation and sale.

Referring to FIG. 4, one exemplary temperature and tension profile forthe system 10 is shown. It should be appreciated that this temperatureand tension profile is not intended to be limiting and other temperatureand tension profiles are contemplated based on the principles outlinedelsewhere herein.

Referring to FIG. 5, this disclosure provides a method 100 of producingan enameled steel sheet having an enamel coating on both sides. Atprocess block 102, the method 100 includes in-line thermal flattening afeed stock steel sheet. The in-line thermal flattening of process block102 thereby produces a thermally-flattened steel sheet. At process block104, the method 100 includes enamel coating the thermally-flattenedsteel sheet on both sides. The enamel coating of process block 104thereby produces the enameled steel sheet having the enamel coating onboth sides. The enamel coating of process block 104 is subsequent to thein-line thermal flattening of process block 102.

Executing the enamel coating of process block 104 directly to the feedstock steel sheet without the in-line thermal flattening of processblock 102 produces a comparison enameled steel sheet. The comparisonenameled steel sheet has properties that are inferior to the product ofthe method 100.

As one example, the comparison enameled steel sheet has a maximumdeviation from flat of 0.5 mm or greater when a pressure of 20 kg/m² isapplied. The enameled steel sheet produced by the method 100 has amaximum deviation from flat of less than 0.5 mm when a pressure of 20kg/m² is applied. In some cases, the enameled steel sheet produced bythe method 100 has a maximum deviation from flat of less than 0.5 mmwhen a pressure of 10 kg/m² is applied.

Maximum deviation can be measured by methods known to those havingordinary skill in the art. In one such method, the pressure is appliedby setting a series of blocks having the proper weight to apply thedesired force atop a sheet of interest that is itself resting on a flatsurface. Once the blocks are placed, a point of greatest deviation fromflat (or multiple points of greatest deviation if it is unclear whichpoint is greater) are identified by human or automated visualization.The magnitude of that deviation is measured by distance measuringmethods known to those having ordinary skill in the art (e.g., laserdistance measurements, a ruler, a caliper, etc.).

The in-line thermal flattening of process block 102 includes heating thefeed stock steel to a predetermined annealing temperature under apredetermined annealing tension. The predetermined annealing temperaturecan be between 300° C. and 700° C., including but not limited to,between 350° C. and 650° C. or between 400° C. and 600° C. Thepredetermined annealing tension can be between 20 MPa and 100 MPa,including but not limited to, between 25 MPa and 75 MPa, between 30 MPaand 50 MPa, or between 35 MPa and 40 MPa. The in-line thermal flatteningof process block 102 can be done in a predetermined atmosphere. In somecases, the predetermined atmosphere can be air.

The enamel coating process of process block 104 can be a two-step,two-fire enameling process. The two-step, two-fire enameling process caninclude applying a ceramic slurry to both sides of a steel sheet andheating the sheet to predetermined enameling temperature whilemaintaining a substantially catenary position over a predetermined spandistance at a predetermined lateral tension. This process is thenrepeated with application of the slurry to only one side of the steelsheet. The predetermined enameling temperature can be between 700° C.and 1000° C. The predetermined span distance can be between 1.0 m and 40m, including but not limited to, between 2.5 m and 35 m, between 3.0 mand 30 m, between 4.0 and 25 m, or between 4.5 m and 20 m. In somecases, the predetermined span distance can be 4.5 m. The predeterminedlateral tension can be between 2.0 MPa and 3.0 MPa, including 2.5 MPa.While one specific enamel coating process is described here in detail,it is contemplated that the method 100 can be suitable for use withother enamel coating processes known to those having ordinary skill inthe porcelain enameling arts.

The feed stock steel sheet can be cold-rolled steel sheet. Thecold-rolled steel sheet can be batch-annealed. The feed stock steelsheet can have a thickness of between 0.1 mm and 1.0 mm. The feed stocksteel sheet can have a width of between 0.75 m and 2.0 m.

The resulting enamel coating can have a thickness of between 0.01 mm and1.0 mm.

The feed stock steel sheet can be steel that meets the specifications ofA242/A242M version 09a (Reapproved 2016) issued by ASTM International.

Process blocks 102 and 104 are performed in a single facility. Processblock 102 and 104 can be performed in a single processing line.

The method 100 can further include cutting the enameled steel sheet intoindividual units. The cutting can be done by methods known to thosehaving ordinary skill in the art.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, certain embodiments of the disclosures described herein canbe embodied within a form that does not provide all of the features andbenefits set forth herein, as some features can be used or practicedseparately from others. The scope of certain disclosures disclosedherein is indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

We claim:
 1. A method of producing an enameled steel sheet having anenamel coating on both sides, the method comprising: a) in-line thermalflattening a feed stock steel sheet, thereby producing athermally-flattened steel sheet; and b) subsequent to step a), enamelcoating the thermally-flattened steel sheet on both sides, therebyproducing the enameled steel sheet having the enamel coating on bothsides, wherein executing the enamel coating of step b) directly to thefeed stock steel sheet without the in-line thermal flattening of step a)produces a comparison enameled steel sheet having the enamel coating onboth side, the comparison enameled steel sheet having a maximumdeviation from flat of 0.5 mm or greater when a pressure of 20 kg/m² isapplied, the enameled steel sheet having a maximum deviation from flatof less than 0.5 mm when a pressure of 20 kg/m² is applied.
 2. Themethod of claim 1, wherein the in-line thermal flattening of step a)includes heating the feed stock steel to a predetermined temperatureunder a predetermined tension.
 3. The method of claim 1, wherein thein-line thermal flattening of step a) is performed in a predeterminedatmosphere.
 4. The method of claim 3, wherein the predeterminedatmosphere is air.
 5. The method of claim 2, wherein the predeterminedtemperature is between 300° C. and 700° C.
 6. The method of claim 2,wherein the predetermined tension is between 20 MPa and 100 MPa.
 7. Themethod of claim 1, wherein the enamel coating of step b) is a two-step,two-fire enameling process.
 8. The method of claim 7, wherein thetwo-step, two-fire enameling process includes the following steps: w)applying a first ceramic slurry to a first side of an input steel sheet,the input steel sheet having a second side opposite the first side, andoptionally applying the first ceramic slurry to the second side of theinput steel sheet, thereby resulting in a first slurried steel sheet; x)heating the first slurried steel sheet to a temperature of between 700°C. and 1000° C. while maintaining the first slurried steel sheet in asubstantially catenary position with the first side or the second sidepointing upward over a span of between 1.0 m and 40 m and a lateraltension of between 2.0 MPa and 3.0 MPa, thereby resulting in a firstcoated steel sheet; y) applying a second ceramic slurry to the firstside or the second side of the first coated steel sheet, therebyresulting in a second slurried steel sheet; z) heating the secondslurried steel sheet to a temperature of between 700° C. and 1000° C.while maintaining the first slurried steel sheet in a substantiallycatenary position with the first side or the second side pointing upwardover a span of between 1.0 m and 40 m and a lateral tension of between2.0 MPa and 3.0 MPa, thereby resulting in a two-step, two-fire enameledsteel sheet, the thermally-flattened steel sheet is the input steelsheet and the enameled steel sheet having the enamel coating on bothsides is the two-step, two-fire enameled steel sheet for the enamelcoating of step b), and the feed stock steel sheet is the input steelsheet and the comparison enameled steel sheet is the two-step, two-fireenameled steel sheet for the executing the enamel coating of step b)directly to the feed stock steel sheet without the in-line thermalflattening of step a).
 9. The method of claim 1, the enameled steelsheet having a maximum deviation from flat of less than 0.5 mm when apressure of 10 kg/m² is applied.
 10. The method of claim 1, wherein thefeed stock steel sheet is a cold-rolled steel sheet.
 11. The method ofclaim 10, wherein the cold-rolled steel sheet is batch-annealed.
 12. Themethod of claim 1, wherein the feed stock steel sheet has a thickness ofbetween 0.1 mm to 1.0 mm.
 13. The method of claim 1, wherein the feedstock steel sheet has a width of between 0.75 m to 2.0 m.
 14. The methodof claim 1, wherein the enamel coating of step b) provides the enamelcoating with a thickness of between 0.01 mm and 1.0 mm.
 15. The methodof claim 1, wherein steps a) and b) are performed in a single facility.16. The method of claim 1, wherein steps a) and b) are performed in asingle processing line.
 17. The method of claim 1, the method furthercomprising cutting the enameled steel sheet into individual units.
 18. Asystem comprising: a source zone for receiving a source product to beprocessed; an in-line thermal flattening zone downstream of the sourcezone; a two-side enameling zone downstream of the in-line thermalflattening zone; and a product removal zone for removing finishedproducts from the system, the product removal zone downstream of thetwo-side enameling zone.
 19. The system of claim 18, wherein the in-linethermal flattening zone includes a furnace and at least two tensioningrolls.
 20. The system of claim 19, wherein the at least two tensioningrolls are configured to establish and maintain a tension of between 20MPa and 40 MPa for steel sheets passing through the in-line thermalflattening zone.
 21. The system of claim 19, wherein the furnaceincludes a thermal flattening heat source.
 22. The system of claim 21,wherein the thermal flattening heat source is configured to establishand maintain a temperature of between 300° C. and 700° C. for steelsheets passing through the in-line thermal flattening zone.
 23. Thesystem of claim 18, wherein the two-side enameling zone includes a firstslurry applicator, a first furnace catenary, a second slurry applicator,and a second furnace catenary, the first slurry applicator upstream ofthe first furnace catenary, the first furnace catenary is upstream ofthe second slurry applicator, the second slurry applicator is upstreamof the second furnace catenary.
 24. The system of claim 23, the two-sideenameling zone including a first heat source and a second heat source,the first heat source configured to heat material within the firstfurnace catenary to a first predetermined temperature, the second heatsource configured to heat material within the second furnace catenary toa second predetermined temperature.
 25. The system of claim 23, whereinthe first predetermined temperature and/or the second predeterminedtemperature is between 700° C. and 1000° C.
 26. The system of claim 23,wherein the first heat source and/or the second heat source is a radianttube.
 27. The system of claim 26, wherein the radiant tube is naturalgas fired.
 28. The system of claim 23, wherein the first furnacecatenary is housed in a first furnace and the second furnace catenary ishoused in a second furnace.
 29. The system of claim 28, wherein thefirst furnace provides a first isolated atmosphere and the secondfurnace provides a second isolated atmosphere.
 30. The system of claim23, wherein the first furnace catenary and/or the second furnacecatenary is configured to have a span of between 1.0 m and 40 m.
 31. Thesystem of claim 23, wherein the first furnace catenary and/or the secondfurnace catenary is configured to maintain a lateral tension of between2.0 MPa and 3.0 MPa.
 32. The system of claim 18, wherein the system isconfigured to receive a feed stock steel, pass the feed stock steelthrough the in-line thermal flattening zone and the two-side enamelingzone, and produce an enameled steel sheet, the enameled steel sheethaving a maximum deviation from flat of less than 0.5 mm when a pressureof 20 kg/m² is applied, wherein passing the feed stock steel through thetwo-side enameling zone without passing through the in-line thermalflattening zone produces a comparison enameled steel sheet, thecomparison enameled steel sheet having a maximum deviation from flat of0.5 mm or greater when a pressure of 20 kg/m² is applied.